This invention relates to a method of controlling exposure in electrophotography and more particularly to a method of controlling the light which is made incident on a photosensitive body in a electrophotographic copying machine.
One of the functions of an exposure controlling device for a photosensitive body, for example, in an electrophotographic copying machine is to use filters and the like to adjust the spectroscopic radiation intensity of the light beam from a source according to its spectroscopic sensitiveity characteristics so as to correct the color reproduction characteristics of the copy. For example, the spectroscopic sensitivity of a Se-type photosensitive body is higher on the side of shorter wavelengths and lower on the side of longer wavelengths as shown by a solid line in FIG. 3. If a beam of light having a flat spectroscopic radiation intensity characteristics is used directly as incident light, therefor, reproduction of blue originals becomes difficult because sensitivity is too high on the short wavelength side. In a situation like this, use may be made of a filter in the exposed device or a lens in the optical system may be coated such that the light on the side of shorter wavelengths is absorbed, or its spectroscopic radiation intensity is lowered on the side of shorter wavelengths, thereby improving the color reproduction in copies.
As another example, the spectroscopic sensitivity of photosensitive bodies using OPC (organic photosensitive compounds) is high on the longer wavelength side and low on the shorter wavelength side within the visible range. In this case, reproduction of red originals becomes difficult because sensitivity is too high on the longer wavelength side as shown by a solid line in FIG. 4 and use may be made likewise of a filter or a lens coating to reduce the spectroscopic radiation intensity of the exposure light in the longer wavelength region as shown by a broken line in FIG. 4.
With some photosensitive bodies using recently developed OPCs and amorphous silicon, however, the spectroscopic sensitivity is flat not only within the visible range but also in both the shorter and longer wavelength regions outside the visible range. If a conventional exposure device were used to reduce the spectroscopic radiation intensity on both the longer and shorter wavelength sides as shown by a broken line in FIG. 5 and to correct the color reproduction in copies when such a photosensitive body is irradiated, its sensitivity outside the visible range would be wasted and the actual overall sensitivity would not be improved from the original sensitivity of the photosensitive body.